class Duixiang{
  /** 
   * dart中的对象操作符
   * ?  条件运算符
   * as 类型转换
   * is 判断
   * 
  */
  
  String name = "条件运算符";
  Duixiang(this.name);
  void show(){
    print("name?:$name");
  }
}